The present invention relates to a method of forming cooperative concave and convex patterns on the working surfaces of complimentary embossing rolls or pressing dies; etc.
To form an embossing pattern on a metal sheet, it is necessary to form the concave and convex patterns as the matrices corresponding to the embossing pattern, and in order that the resulting embossing to be made smoothly, it is necessary to predetermine the concavity on the working surface opposing and cooperating with the working surface having the convexity such that a clearance equal to the thickness of the work-piece is provided. If the correct clearance is not provided, the work-piece would be broken or sheared as it is pressed. It is, however, very difficult to form the working surfaces of the steel rolls or dies in concave and convex patterns with the clearance equal to the thickness of the metal sheet provided there-between, and it is well nigh impossible to do so especially when complex, arbitrary or unusual patterns are chosen.
Heretofore, as the metal stock to be worked, soft aluminum sheet or very thin steel sheet has been chosen; it was passed while pressing between a steel roll on which the concave-convex pattern was formed, on one hand, and a soft roll with smooth surface of compressed paper, rubber, etc., on the other, to let the metal sheet worked undergo a plastic deformation, taking advantage of the surface deformation of the soft-roll, thereby forming the embossed pattern.
A working method of this type has proven most disadvantageous, however, because the working surface of one of the rolls is soft, and thick steel and stainless steel could not be worked. Moreover, the forming dies were excessively consumed due to wear
In order to form a pattern on thick metal sheets in general or thick stainless sheets in particular, it is necessary to use steel rolls with high rigidity for both working rolls, but the process of forming the same pattern symmetrically on two steel rolls with a clearance equal to the thickness of the work-piece provided on one of the rolls involves the difficulty mentioned above. For this reason, hitherto, embossed patterns could not be formed on thick steel sheets and thick stainless sheets, with satisfactory results.